Dialkyl-N-cyanoimidocarbonates are valuable synthesis components for the preparation of substituted cyanoguanidine compounds. In this way, by means of successive substitution of the alkoxy radicals, it is also possible to obtain asymmetrically substituted cyanoguanidine compounds, which can be used, inter alia, as histamine 2H antagonists.
In many cases, dialkyl-N-cyanoimidocarbonates can replace previously employed reagents, such as dimethyl-N-cyanoimidodithiocarbonates (see J. Org. Chem., Vol. 39, No. 11, 1522 et seq./1974) or diphenyl-N-cyanoimidocarbonate, whereby the formation of by-products which are difficult to deal with and/or dangerous to health are avoided and improved yields are obtained.
The synthesis of diethyl N-cyanoimidocarbonate by the reaction of isolated diethyl imidocarbonate with cyanamide under anhydrous conditions has already been described (see Chem. Ber., 100, 2604/1967). In this case, a yield of only 69% of crude product was obtained which, for purification, has to be recrystallised from anhydrous diethyl ether.
In EP 0 014 064 B1, there is described a process for the preparation of disubstituted dimethyl or diethyl N-cyanoimidocarbonates by the reaction of an appropriately substituted imidocarbonate with cyanamide in a two-phase system which contains water and an organic solvent which is not miscible with water, for example toluene.
In DE-OS 32 25 249, there is described a process according to which sodium cyanide is reacted under alkaline conditions with an appropriate alcohol, subsequently chlorine is passed in and, after neutralisation of the reaction mixture and addition of cyanamide, the substituted N-cyanoimidocarbonate formed is, after the addition of methylene chloride, obtained from the organic phase.
The above-described processes suffer from the disadvantage that, in the case of the preparation, either health-endangering by-products are formed or organic solvents, some of which are chlorinated, are needed which require special expense for the removal thereof after the reaction has taken place.